Commercial refrigeration systems are used, for example, to provide the large refrigeration requirements in a supermarket installation. Industrial refrigeration systems are used, for example, for operation in refrigerated warehousing, ice plants and like installations. Environmental control systems are used, for example, for effecting the space air heating, ventilating and air conditioning in various commercial and industrial installations. These systems include local electrical or electro-mechanical control apparatus for operating the system components. In commercial and industrial refrigeration systems, the local control apparatus senses temperature and pressure, compressor oil levels, condensing requirements, evaporator defrost needs and the like component operating conditions. The local control apparatus operates the controlled system components in response to such sensed conditions to provide efficient refrigeration while also providing safety features to compensate for compressor overloading, high and low pressure limits, low oil levels, etc. In environmental control systems, the local control apparatus senses temperature and humidity conditions and operates the controlled heating, air conditioning and/or ventilating components to provide optimum comfort levels and the like.
There is now a proliferation of electronic remote controllers available for connection with such commercial and industrial refrigeration and/or environmental control systems. Such remote controllers are generally part of an energy management system, which operates the entire controlled system and separate system components thereof according to environmental and/or other external parameters in order to use the system in the most efficient manner with minimum power usage. Frequently, such remote controllers are designed to operate several systems in a coordinated manner in order to achieve a particular, desired result. For instance, a remote controller having a microprocessor may be programmed to operate all refrigeration systems in a supermarket installation, and also efficiently operate the environmental air handler package containing heating and air conditioning for controlling the temperature and humidity of the store's space air.
Heretofore, the remote electrical controller most frequently has been incompatible with the local control apparatus and/or the external control ports of the system components, such as compressors, condenser fans, etc. This incompatibility may be the result of a local control and controlled system which is made by a different manufacturer than the remote electrical controller. For example, the inputs which are used to control the compressor motors of a refrigeration system may have different electrical characteristics than the outputs of the remote controller.
Additionally, the remote controller is, in many cases, connected directly in series with the local control apparatus and may override or inhibit safety limit circuits incorporated in the local control apparatus for protection of the equipment, such as motor compressor overheating and high pressure limit cutout. Such connection of the remote controller to the local control apparatus will affect the safety or limit circuits and negate their intended safety purpose. For safety reasons, the remote controller should be electrically isolated from the local control apparatus. This isolation is required so that the local control apparatus may operate as a self-contained unit or operate under the primary control of the remote controller without an interconnection between the respective power systems of the local control apparatus and the remote controller. Remote controller operation must also be accomplished with the failsafe condition of control by the local control apparatus. Thus, in the event of remote controller failure, the local apparatus must be able to take back control of the system from the remote controller in order to insure the reliable and safe operation of the controlled system while preventing simultaneous control by the remote and the local controllers.
It is now recognized that the remote controller should be provided with monitoring signals to verify and execute its control routine. For example, the compressor status (on or off) must be communicated to the remote controller in order that the remote controller can verify that there is an appropriate response by the refrigeration or air conditioning system which it is operating.
U.S. Pat. No. 3,871,443 to Jones describes a safety control for a remote control system. The remote system turns a zone heating and cooling air conditioning system unit on and off from a central control point. A safety freeze control system simultaneously switches the unit from a normal operating mode to a heating mode at a predetermined temperature and overrides the remote control system. The remote control of Jones, as with the other prior art, does not monitor the local unit and does not permit comprehensive remote control over the local unit in substitution for local control.
U.S. Pat. No. 4,206,612 to Gardner discloses a refrigeration system control. The system contains a compressor supplying refrigerant to several evaporators that are independently operated. Each evaporator has separate controls connected to a master control which prevents all of the evaporators from being defrosted at one time. Among other missing features, no switchback or isolation is suggested.
U.S. Pat. No. 4,272,012 to Molnar et al. describes a method and system for controlling a plurality of temperature conditioning units. The units are sequentially enabled and disabled. A setback feature which can be overridden by a thermostatic control is provided for off hours. An interface with monitoring and isolation is not discussed.
U.S. Pat. No. 4,333,519 to Shafrir et al. shows a controller for air conditioning units. A switch connects the unit to its energy source. In a first mode, the switch interrupts the connection; in a second mode the connection is uninterrupted. A control operates the switch in response to various conditions. However, no switchback or remote control is proposed.